Characterization of HIV Reverse Transcriptases with Tyr181→Cys and Leu100→lle Mutations

Two mutants of human immunodeficiency virus (HIV) reverse transcriptase (RT), Tyr181 to Cys and Leu100 to He, have been prepared and characterized by use of various inhibitors. As compared to wild type RT the mutant RT's had lower Kcat/Km values. The Km values were lower with heteropolymeric than with homopolymeric template-primers. Inhibition by phosphonoformate was of mixed type with both wild-type and mutant RT's and the mutants were less sensitive to phosphonoformate than the wild type RT. The non-nucleoside RT inhibitors 9-CI-TIBO and L-697,661 gave a non-competitive inhibition with respect to substrate of the wild type RT. The mutant RT's were inhibited at higher concentrations, showing a mixed type of inhibition with respect to substrate. ddGTP caused a competitive inhibition of wild type and mutant RT's with respect to substrate. RT preparations with different mutations are useful in rapidly characterizing the interaction between various inhibitors and HIV RT and thus facilitate the development of new inhibitors.

Sequence analysis of proviral HIV RT amplified directly by a semi-quantitative technique from AZT treated patients

To minimise possible arbitrary selective effects of culturing HIV, proviral RT DNA was isolated directly from PBMCs of four patients treated for 6-14 months with AZT. RT DNA was amplified by PCR and sequenced directly without further in vitro manipulation. Eighteen changes additional to those 4 or 5 changes previously shown by genetic reconstruction experiments [Kellam et al.: Proceedings of the National Academy of Sciences of the United States of America 89:1934-1938, 1992] were found in the 14 different sequences analysed. Substitutions clustered in two defined areas of the RT, from amino acids 60 to 70 and from 180 to 220. Mutations were observed at each of the two areas independently or at both sites simultaneously. Amino acid changes in RT from patients harbouring resistant strains of HIV-1 were found in positions 60 (Val), 62 (Ala), 93 (Gly), 100 (Phe), 161 (Pro), 173 (Asn), 177 (Glu), 180 (Ile), 181 (Tyr), 182 (Leu), 186 (Asp), 194 (Gln), 196 (Glu), 200 (Ile), 209 (Val), 210 (Trp), 211 (Lys), and 214 (Phe) in addition to those described previously. It was anticipated that multiple proviral DNAs would be present in a single clinical sample. Therefore end point dilution PCR methodology was used, which allowed sequence analysis of separate proviral DNA molecules from the patients' proviral DNA. Even in patients who had received AZT for more than 10 months wild-type "AZT-sensitive" RTs co-existed with mutated "AZT-resistant" RTs in the same patient sample.